Project Info

SR 104- Hood Canal Bridge - Draw Span

The Hood Canal Bridge draw spans are the two mechanically movable floating bridge pontoons that retract to allow marine traffic that can’t make it under the bridge’s transition spans to travel through Hood Canal. The draw spans are located between the bridge’s two control towers.

HOW DOES THE DRAW SPAN WORK? Near the center of the channel, the Hood Canal Bridge features two sets of identical draw spans and lift spans on the east and west sides. When the bridge is closed, the concrete draw span pontoons and grated lift spans serve as the roadway.

To open, hydraulic cylinders raise the lift span roadway sections about six feet so the draw span pontoons can then retract beneath them. Gears move the pontoons along while rollers help guide the pontoon into the space under the lift spans.

To close, the process is simply reversed as the draw span pontoons are extended and the lift spans lowered to become a usable roadway again.Watch the west-half draw span open:When the west-half draw span opens, this 300-foot floating pontoons is moved back into a space directly under a 300-foot section of the bridge road deck near the west control tower. The road deck is lifted about 6 feet into the air to allow for the west draw pontoon to slide under it.

Watch the old east-half draw span open: The old east-half draw span featured a pontoon lagoon around a bulge in the roadway. The 300-foot draw span pontoon ponton was moved back into the “bulge” area between the roadway pontoons near the east control tower.

NEW EAST-HALF DRAW SPANThe new east-half draw span will be identical in design to the current west half draw span, making travel on the bridge safer by removing the “bulge” in the east side roadway.

The new east-half draw span is made up of 10 different pontoons. Pontoons PA, PB, Q, NA and NB were assembled together at Todd Shipyards in Seattle to form a “U” shape area around the location where the draw span retractable assembly units pull back.

Then pontoons YD, YE and YF were lowered under water, positioned underneath the other pontoons and connected.

When the third cycle of pontoon construction is completed, the two pontoons that make up the retracting section of the draw span will be connected together and assembled with the other eight draw span pontoons.